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Project background and reasons
Yuanshantz Flood Diversion Tunnel of Keelung River is located in Ruifang District, New Taipei City, Taiwan. Avoiding the flooding in downstream area of Keelung River is the value of this tunnel. When the flood strikes, part of the flood is diverted to the tunnel. As a result, the flood risk in downstream area of Keelung River can be mitigated.
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Design principles
The flood can be automatically diverted by the unmanned tunnel on the basis of the principle of natural overbank flow. Two sand drainage tunnels are constructed in order to facilitate the removal of the deposition in grit chamber and reduce the times of flood diversion.
Considering the safety of the tunnel and the maximum possible flood discharge, a 12m diameter tunnel is used in order to reduce the flood amount in the downstream of Keelung River, where the flood discharge is 1,310cms and the maximum discharge of the downstream is 310cms.
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Structure arrangement
The flood diversion project is divided into four sub-structures: the diversion weir, the inlet structure, the flood diversion tunnel and the outlet structure. The upstream inlet structure should precisely lead the diversion flood to the diversion tunnel. Therefore the location of the inlet structure is the most important part of this project. Once the location of inlet structure is determined, other structures could be placed in the proper location according to the location of the inlet structure.